Intramolecular charge transfer in 4-aminobenzonitriles does not necessarily need the twist
Intramolecular charge transfer in 4-aminobenzonitriles does not necessarily need the twist
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DOI：
10.1021/ja042413w
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发表时间：
2005-05-18
影响因子：
15
通讯作者：
Robb, MA
中科院分区：
文献类型：
--
作者：
Gómez, I;Reguero, M;Robb, MA
在电子给体/受体物质如4-（二甲氨基）苯甲腈（DMABN）中，激发到S-2态之后是内部转换到局部激发（LE）态。双荧光，然后成为可能的LE和扭曲的分子内电荷转移（TICT）状态。本文提出了DMABN和4-氨基苯甲腈（ABN）ICT反应的详细机理。这两个发光的Si物种是沿着氨基扭转反应坐标键合的。然而，S-2/S-1 CT-LE无辐射衰变是通过一个几乎平行于这个扭转坐标的延伸圆锥形相交"缝"发生的。在该锥形交叉接缝上的最低能量点处，氨基未扭转;然而，接缝可用于大范围的扭转角。因此，S-1 LE-TICT平衡和双荧光将由（a）S扭转反应路径和（B）沿着氨基扭转坐标发生S-2/S-1 CT-LE无辐射衰变的位置控制。对于DMABN，LE和TICT的群体可以发生，因为这两个物种具有相似的稳定性。然而，在ABN中，平衡有利于LE，因为在高得多的能量下发现了TICT状态，其中LE的反应势垒低。这解释了为什么在ABN中不能观察到双重荧光。研究了从LE态进入的S-1-> S-0失活通道。
In electron donor/acceptor species such as 4-(dimethylamino)benzonitrile (DMABN), the excitation to the S-2 state is followed by internal conversion to the locally excited (LE) state. Dual fluorescence then becomes possible from both the LE and the twisted intramolecular charge-transfer (TICT) states. A detailed mechanism for the ICT of DMABN and 4-aminobenzonitrile (ABN) is presented in this work. The two emitting Si species are adiabatically linked along the amino torsion reaction coordinate. However, the S-2/S-1 CT-LE radiationless decay occurs via an extended conical intersection "seam" that runs almost parallel to this torsional coordinate. At the lowest energy point on this conical intersection seam, the amino group is untwisted; however, the seam is accessible for a large range of torsional angles. Thus, the S-1 LE-TICT equilibration and dual fluorescence will be controlled by (a) the S, torsional reaction path and (b) the position along the amino group twist coordinate where the S-2/S-1 CT-LE radiationless decay occurs. For DMABN, population of LE and TICT can occur because the two species have similar stabilities. However, in ABN, the equilibrium lies in favor of LE, as a TICT state was found at much higher energy with a low reaction barrier toward LE. This explains why dual fluorescence cannot be observed in ABN. The S-1 -> S-0 deactivation channel accessible from the LE state was also studied.